Out of 10 million users that's a very impressive number. People had been worrying about "check-in fatigue" -- the idea that Foursquare would pick up new users because they want to check out the app, but after a while they would stop using it.

Now, 3 million check-ins per day doesn't mean 3 million users use it every day, because we're sure plenty of people check-in several times a day, but it's still a number that suggests high engagement overall, and mitigates worries about check-in fatigue.

Also, Crowley said Foursquare has signed up 500,000 merchants. The vast majority of these merchants, perhaps even all of them, don't pay anything, because Foursquare isn't charging them anything. But Foursquare doesn't need revenue at this point anyway. What it does mean is that merchants are at least curious about and interested in using Foursquare to connect with their customers.

And because Foursquare doesn't have Groupon's thousands-strong sales force, it means it accomplished most of that through word-of-mouth.